I. Field of the Invention
The present invention relates to a photopolymerizable composition and, more particularly, to a photopolymerizable composition based on an epoxy compound.
II. Description of the Prior Art
Epoxy resins are frequently used as insulating materials or photoresist materials for electrical equipment. Epoxy resins are conventionally cured by heat. However, efforts have been recently made to photocure an epoxy resin from the viewpoints of energy conservation and workability.
A method of photocuring an epoxy resin is known which comprises denaturing the epoxy resin with a compound having a photopolymerizable group such as vinyl group, and photocuring the photopolymerizable group. However, the denatured epoxy resin which is cured by this method is inferior in heat resistance to the cured body of the original epoxy resin.
Another method of photocuring an epoxy resin is also known which comprises adding a photodecomposable catalyst to the epoxy resin and photodecomposing the catalyst to thereby cure the epoxy resin. Examples of such catalysts include complex catalysts such as Ph.sub.3 S.sup.+ PF.sub.6.sup.- or Ph.sub.2 X.sup.+ BF.sub.4.sup.- (where Ph is phenyl group and X is a halogen). Although these photodecomposable catalysts provide a cured epoxy resin which has excellent mechanical characteristics and heat resistance, ions of the components of these catalysts remain within the cured epoxy resin. These ions thus adversely affect the electrical characteristics of electrical equipment coated with such a cured epoxy resin, or cause corrosion.